This invention relates to saw straightening and tensioning, and more specifically to a novel method and machine for detecting and correcting tension defects in a circular saw blade, and providing a proper distribution of tension so that the blade will run straight and true at cutting speeds.
A thorough discussion of the problems involved in tensioning saw blades appears in my prior U.S. Pat. Nos. 3,964,348 issued June 22, 1976, and 4,027,531 and issued June 7, 1977. Those patents generally disclose and claim a method of detecting and correcting tension levels in a saw blade by elastically bowing the blade toward a curved locus having a contour to which the blade would fully conform if it were properly tensioned and straightened. The method then involves sensing deviations of the blade surface from the proper curved locus.
The preferred practice is to bow the blade into the approximate form of a segment of a right-circular cylinder, that is, to bow it around an axis parallel to a diameter of the blade but spaced apart along the major rotational axis of the blade from its surface. This is done by pressing axially at the center of the blade in one axial direction, while pressing in the opposite axial direction at two points near diametrally opposite edges of the blade and aligned on a common diameter. The resulting curvature takes place in a family of planes parallel to a plane defined by this common diameter and the rotational axis of the blade; while there is no substantial curvature in perpendicular planes parallel to the rotational axis of the blade.
Detection of the resulting curvature is therefore carried out along a curved path, which at least approximately lies in a plane defined by the common diameter of pressure application and the rotational axis. This method is effective and satisfactory, but does require a relatively sophisticated and well-adjusted mechanism capable of sweeping the sensor accurately through the proper curved path. Since the proper curvature is altered by a change in any of several parameters, including blade diameter, thickness, material, and desired overall tension distribution, careful readjustment is called for when batches of different blades with different specifications are to be processed.